I believe the answer is: D. a change in the cost of inputs changes how much a producer will supply at a given price
Fertilizer is considered to be an input for the avocado since it is an integral part for the avocado producers to transform raw material (Avocado seeds) into a finished product (full grown avocado), Which mean when the cost of fertilizer is increased, the amount of capital needed before their avocado is ready to sell would also increased.